Integrated engine exhaust emission control system

ABSTRACT

An integrated method for controlling and preventing the emission of noxious components in engine exhaust during all the various phases of the engine operating cycle, such as startup, normal operation, overload, and when the engine exhaust gas is at an abnormally elevated temperature.

Unite States Patent Tourteilotte et al.

INTEGRATED ENGINE EXHAUST EMISSION CONTROL SYSTEM Inventors: John F.Tourtellotte, Westfield; John S. Negra, Plainfield; Abe Warshaw,Matawan; John F. Villiers-Fisher, Kendall Park, all of NJ.

[451 Sept. 11, 1973 3,662,540 5/1972 Murphey 60/274 1,902,160 3/1933Frazer..... 60/301 2,673,446 3/1954 Salardi.... 60/297 2,942,932 6/1960Elliott 60/297 3,050,935 8/1962 Eastwood... 60/286 3,180,712 4/1965I-Iamblin 60/284 3,228,746 1/1966 Howk 60/298 Primary Examiner-DouglasHart Altorney.1. L. Chaboty [57] ABSTRACT An integrated method forcontrolling and preventing the emission of noxious components in engineexhaust during all the various phases of the engine operating cycle,such as startup, normal operation, overload, and when the engine exhaustgas is at an abnormally elevated temperature. 1

20 Claims, 1 Drawing Figure SECONDARY AIR 'gLowsR EXHAUST MANIFOLDEXHAUST MANIFOLD BED 1 INTEGRATED ENGINE EXHAUST EMISSION CONTROL SYSTEMBACKGROUND OF THE INVENTION biles, trucks, buses or the like. In recentyears it has been recognized that the exhaust gas discharged frominternal combustion engines is a serious source of air pollution,especially in metropolitan areas. In some areas a so-called smog isgenerated due to atmospheric inversions and accumulation of such exhaustgases in the atmosphere. Recent attempts to prevent such air pollutionhave concentrated on the destruction or elimination of noxiouscomponents by catalysis, especially by admixture of secondary air intothe exhaust gas after initial catalytic reduction of nitrogen oxides,followed by catalytic oxidation of residual hydrocarbons, carbonmonoxide, etc., in various types of apparatus or catalytic mufflersespecially designed for this purpose.

The invention relates particularly to catalytic exhaust gas treatmentsystems in which air is added to the exhaust gas, and the resultingmixture is passed through a catalyst bed or beds to catalyticallyoxidize noxious unburned or thermally degraded hydrocarbon vapors orother organic vapors, and carbon monoxide, to innocuous products such ascarbon dioxide and water vapor. The term hydrocarbons will be understoodto encompass and include residual unburned hydrocarbons, thermallydegraded hydrocarbons and other organic vapors in the exhaust gasstream. The invention also relates to systems in which the exhaust gasis initally passed through a reducing catalyst bed to selectively reducenitrogen oxides to nitrogen by catalytic reaction with carbon monoxide,hydrogen and/or hydrocarbons, which may be initially present in theexhaust gas.

The catalytic reduction-oxidation procedure, during steady stateoperation with a hot engine and hot exhaust gas, results in theelimination of these deleterious components initially present in theexhaust gas from external or internal combustion engines such as jetengines, gas turbines, diesel engines, and gasoline-burning automobile,bus and truck engines, so as to prevent the discharge into theatmosphere of these noxious components including unburned hydrocarbons,other organic vapors, carbon monoxide and nitrogen oxides, and therebyprevent air pollution.

2. Description of the Prior Art Numerous catalysts, catalytic devicesand mufflers, and treatment systems have been proposed for theprocessing of exhaust gas emitted by engines, so as to control engineexhaust emissions and prevent the discharge of noxious components intothe atmosphere. Among the many patents relating to catalysis andcatalytic formulations may be mentioned U.S. Pats. Nos. 3,053,773;3,429,656; 3,316,057; 3,398,101; 3,477,893 and 3,476,508, and U.S.Patent Application Nos. 55,998 filed July 17, 1970 and 45,576 filed June11, 1970 now U.S. Pat. No. 3,701,822. Apparatus for carrying out theprocedure are described in U.S. Pats. Nos. 3,380,810; 3,325,256;3,255,123; 3,222,140; 3,186,806; 3,180,712; 3,169,836; 3,168,806;3,146,073 and 3,086,839 and U.S. Patent Application No. 33,359 filedApr. 30, 1970, now U.S. Pat. No. 3,656,915, which describes a two-stageapparatus for carrying out the process with interstage air injection.

SUMMARY OF THE INVENTION In summary, the method of the present inventionentails the control of engine exhaust emissions in a system in which theinitial exhaust gas stream emitted by the engine contains noxiousimpurities including nitrogen oxides, hydrocarbons and carbon monoxide,and the initial exhaust gas stream is passed through a reducing catalystbed and an oxidized catalyst bed, with secondary air injection prior tothe oxidizing catalyst bed. Four time periods or cycles are contemplatedin the preferred embodiment of the invention as described in detailinfra.

In the first time period starting with engine startup and extending forup to 10 minutes, the initial exhaust gas is at a temperature below 250C and contains an abnormally high concentration of hydrocarbons.Secondary air is injected prior to thereducing catalyst bed and thecatalytically treated exhaust gas is passed through a hydrocarbonabsorbent bed.

In the second time period, the engine is operated nor; mally and exhaustgas is produced at 250 to 700 C. The secondary air injection prior tothe reducing catalyst bed is reduced or terminated, so that free oxygencontent of the exhaust gas at entry into the reducing catalyst bed isless than about 30 percent in excess of the stoichiometric requirementto oxidize carbon monoxide in the exhaust gas, and additional secondaryair is injected between the reducing and the oxidizing catalyst beds. Inaddition, a portion of the hot exhaust gas discharged from the oxidizingcatalyst bed is recycled through the hydrocarbon absorbent bed to desorbhydrocarbons, and the resulting gaseous mixture is recycled to theengine.

During a third time period of engine overload, in which the initialexhaust gas temperature is in the range of 700 to l,000 C, the initialexhaust gas stream is cooled prior to the reducing catalyst bed byindirect heat exchange with the surrounding atmosphere, by passing theexhaust gas stream through an overtemperature control loop or othermeans adapted to receive and cool exhaust gas. Other operatingconditions and flow sequences during the third time period remain asprovided in the second time period.

During a fourth time period of severe engine overload, in which theexhaust gas is generated at a temperature in excess of l,000 C, allsecondary air flow is terminated, and the flow of recycle exhaust gasthrough the absorbent bed is also terminated;

The invention, in a preferred embodiment, consists of a complete controlsystem to reduce the emissions in the exhaust of internal combustionengines, and other fuel burning equipment. The invention specificallyreduces the emissions of oxides of nitrogen, hydrocarbons and carbonmonoxide. The invention converts these obnoxious gases to harmlessnitrogen gas, water vapor and carbon dioxide gases. The FederalGovernment of the United States has set standards relating to theemissions from automobiles and to the methods of analyging theseemissions. In addition to reducing the emissions to low levels, it isnecessary for the system to begin operation immediately upon startingthe engine. Catalytic systems are capable of obtaining these low levelsof emissions, but must be hot before they operate efficiently. Thepresent invention solves the problem by the development of hardware anda control system to warm the system to operating temperatures in a shorttime; hardware and control system to capture unburned hydrocarbons earlyin the cycle; a cooling system to prevent overtemperature damage to thehardware, catalyst and control components; and the hardware and controlsystem to recycle the unburned hydrocarbon, captured during the firstfew minutes after engine startup, back to the engine inlet during normaloperation of the engine.

The system components preferably include an air pump or pumps driven bythe fan belt off the engine crankshaft, manifold air injection pipingfrom an air pump for injection of air into the exhaust ports or manifoldof the engine, an overtemperature cooling loop with a bypass pipe andvalve, a catalytic converter including a first bed of catalyst capableof reducing nitrogen oxides to nitrogen, carbon dioxide and water vaporby reaction with reducing gas components such as carbon monoxide andhydrogen which are produced in the engine at appropriate air-fuelratios, air injection ducts to supply oxidizer air from an air pump to asecond catalysis bed, the second catalytic bed being capable ofoxidizing hydrocarbons and carbon monoxide to water vapor and carbondioxide with excess air as the oxidizer supplied by an air pump orblower, an absorbent bed capable of absorbing a wide spectrum ofhydrocarbons at low temperature, a bypass valve for switching exhaustgas to and from the absorbent bed, an intake to the air filter or intakemanifold, to draw a small portion of hot exhaust gas through thehydrocarbon-laden absorbent bed during normal operation of the engine inorder to regenerate the absorbent, and temperature controls such asthermo-couple probes in the beds to control the system and exhaust gasflow during various stages of the operating cycle.

The principal advantage of the present invention is that the emission ofnoxious components in the exhaust gas from an engine is prevented duringall stages of the engine operating cycle. The invention convertsobnoxious gases such as carbon monoxide, nitrogen oxides, and unburnthydrocarbons, which are classified by the Federal Government of theUnited States as major atmospheric pollutants, into harmlessnon-pollutants, such as water vapor, carbon dioxide and nitrogen. Theinvention permits the existing highly refined internal combustion enginenow used to propel automobiles to remain essentially intact. The controlsystem replaces the exhaust muffler system of the present engines, andwith only one moving part, the air pump or blower, the control systemremoves the pollutants and eliminates obnoxious engine noise and airpollution. The system of the present invention has overcome the problemof cold engine startup which is a condition of high emission for theinternal combustion engine and for most other emission control systems.The system of the present invention is simple in its operation, compactin size, low in initial cost and low in maintenance. The system employscatalyst compositions consisting of non-noble metals, which are notclassified as pollutants or harmful to life. Novel features of theinvention include the control of emissions from the moment the engine isstarted, even with a cold engine; control of emissions for the entiredriving cycle; self-regeneration of the system; a built-inovertemperature control to prevent seifdestruction of the system underall load conditions; and

ability to tolerate a wide range of engine exhaust gas compositions.

It is an object of the present invention to provide an improvedintegrated engine exhaust emission control system.

Another object is to prevent air pollution due to the discharge ofnoxious components in engine exhaust gas into the atmosphere.

A further object is to prevent emission of unburned hydrocarbons duringthe initial period of operation of a cold engine, when there is a highlevel of unburned hydrocarbons in the exhaust gas emitted by the engine.

An additional object is to provide an integrated engine exhaust emissioncontrol system which functions at a high level of efficiency during allphases of the engine operating cycle.

These and other objects and advantages of the present invention willbecome evident from the description which follows.

DESCRIPTION OF THE DRAWING AND PREFERRED EMBODIMENTS Referring now tothe drawing, which illustrates the entire integrated engine exhaustemission control sys tem, the system includes engine 1 which is anysuitable internal or external combustion engine, which may be stationaryor mounted on a moving vehicle such as an automobile, bus or truck.Various other types of engines to which the present invention isapplicable are mentioned supra. In this embodiment of the invention,engine 1 is a gasoline-burning internal combustion engine mounted on anautomobile chassis. Startup of the engine 1 causes primary combustionair stream 2 to flow into venturi inductor or aspirator 3, which inductsrecycle gas stream 4 into the engine during normal operation of theengine, as will appear infra. During startup, only stream 2 flowsthrough unit 3 and stream 2 is drawn into air filter 5. The primarycombustion air flows downwards from filter 5 and mixes with fuel stream6, which may be any suitable fluid hydrocarbon such as gasoline or thelike. The resulting combustion mixture flows into the engine intakemanifold, not shown, and thereafter into the engine cylinders.Combustion of the fuel in the engine cylinders generates usable powerand an exhaust gas stream containing noxious components includingnitrogen oxides, hydrocarbons and carbon monoxide. The exhaust gasstream is collected in the exhaust manifolds 7, and during the startupand initial stage of operation of the engine 1, the exhaust gas isdischarged into the manifolds 7 with a high concentration of unburnedhydrocarbons, typically 0.2 to 3.0 percent by volume as compared to anormal concentration of about 0.1 percent or less, and at a temperaturegenerally below 250 C and typically in the range of 50 to 200 C.

During the initial engine operation stage, a relatively large proportionof secondary air is injected into the exhaust manifolds 7, so that aportion of the hydrocarbons and carbon monixide contained in the exhaustgas are oxidized in situ within the manifolds 7 This oxidation reactionwithin manifolds 5 produces two desirabie results, namely elimination ofa portion of the noxious components in the exhaust gas and rapidelevation of the exhaust gas temperature to a suitable level forsubsequent catalysis.

Secondary air stream 8 is inducted into and passes through secondary airblower 9, and is discharged as stream 10, which flows through the valve11 which is fully open during the initial time period of operation ofthe engine. This initial time period, which commences with enginestartup, is generally of a duration of less than minutes and typicallyof a duration of 2 to 6 minutes. The secondary air flows from open valve11 via stream 12, which divides into secondary air portion streams 13and 14, which are passed into the exhaust manifolds 7.

The gaseous mixture of exhaust gas and secondary air formed in manifolds7 is discharged via streams 15, which are at a temperature generallybelow 250 C. Streams 15 combine to form stream 16, which flows duringthe initial startup time period and also during normal operatingconditions via stream 17, open valve 18 and stream 19 to stream 20.

During overload operation of engine 1, such as when engine 1 is under aheavy load due to acceleration or movement of the automobile up a steepgrade, or other abnormal operating conditions, streams 15 may bedischarged at a highly elevated temperature such as in the range of 700to l,000 C. In this case, valve 18 is closed and stream 16 flows viastream 21 and open valve 22 into over-temperature control loop 23, whichtypically consists of a length of pipe preferably-provided with aU-bend. Pipe 23 is exposed to the surrounding atmosphere, typically bybeing mounted below the chassis of the automobile, so that the hotexhaust gas flowing through pipe 23 is cooled by indirect heat exchangewith the surrounding atmosphere to a reduced temperature compared tostream 21. Cooling loop 23 discharges the cooled exhaust gas to stream20.

Stream in any case flows into a bed or plurality of beds of reducingcatalyst within container 24. The reducing catalyst within unit 24 is asuitable reducing catalyst for the reduction of nitrogen oxides toinnocuous nitrogen by reaction with the remaining hydrocarbon vapors,carbon monoxide and/or hydrogen contained in the exhaust gas componentof stream 20. During the initial stage or startup of engine operation,this reaction may not go to completion because of the low temperature ofstream 20 and the resultant low temperature of the catalyst in unit 24.In any case, typical catalysts or catalyst formulations for attainingthis reduction reaction are nickel, cobalt, manganese or copper, ormixtures thereof, deposited on a suitable carrier such as alumina,kaolin, silica, etc. The active metallic constituents may be present inthe catalyst formulation in the metallic state, as oxides or reducedexides, or as salts. Other suitable or conventional catalysts, such asthose specified in the patents and applications enumerated supra, mayalso be employed in unit 24.

The resulting exhaust gas stream 25 discharged from container 24 is nowusually depleted in nitrogen oxides content, however stream 25 containsresidual hydrocarbon vapors together with carbon monoxide. Duringinitial operation of the engine 1, stream 25 flows per se directly intothe oxidizing catalyst bed, however, during normal operation of theengine 1, and overtemperature operation up to an exhaust gas temperatureof about 1,000" C, secondary air is added to stream 25. The secondaryair stream 26 in this case passes via blower 27 as stream 28 throughopen valve 29 and as stream 30 for addition to stream 25 to form stream31. As mentioned supra, during initial operation of the engine 1, stream30 is omitted and streams 25 and 31 are identical.

Stream 31 flows into the oxidizing catalyst bed within container 32,which contains discrete particles of an oxidizing catalyst formulation.During initial operation of the engine 1, a minimal reaction may occurin unit 32 due to low temperature. In any case, stream 31 flows intounit 32, and a catalytic oxidation of at least a portion of thehydrocarbon vapors and carbon monoxide in the gas stream to innocuousproducts such as water vapor and carbon dioxide takes place withincontainer 32. The catalyst bed or beds in unit 32 may be similar oridentical to the catalyst bed in unit 24,-thus the bed in unit 32typically consists of oxides or reduced oxides or salts of nickel,cobalt, manganese or copper, or mixtures thereof, or elemental metalsdeposited on a suitable carrier such as alumina, kaolin, silica or thelike. Other suitable catalysts formulations may be employed in unit 32,such as those described in the patents and applications mentioned supra.During normal operation of the engine 1, when stream 30 is added tostream 25 to form stream 31 with a viable oxygen content typically inthe range of 1 to 10 percent by volume, an exothermic catalytic reactiontakes place in the bed within unit 32 between free oxygen and residualhydrocarbon vapor and/or carbon monoxide, whereby these noxiouscomponents derived from the exhaust gas are oxidized to innocuousreaction products. During the initial time period of operation of theengine 1, only partial or incomplete destruction of hydrocarbon vaportakes place in unit 32.

The temperature of the bed within unit 32 is measured by the temperaturesensitive element 33, which typically consists of a thermometer,thermo-couple, or a fluid filled bulb within the catalyst bed whichtransmits fluid pressure or other suitable signal responsive totemperature, to temperature indicating element 34 which is preferablymounted on the dashboard of the automobile. During initial operation ofthe engine 1, element 34 typically indicates a temperature which isbelow about 250 C in the bed within unit 32, and element 34 alsotransmits a signal or control setting via line 35 to relay 36, whichelectrically or pneumatically transmits a signal to fully open valve 11,to open valve 18 and to close valves 22 and 29. The control signals mayalso be transmitted via a liquid-filled tube or other hydraulic system.During normal operation of the engine 1, relay 36 transmits a signal toat least partially close valve 11, so that the flow of stream 12 isreduced, and so that during normal operation the free oxygen content ofstream 16 is less than about 30 percent in excess of the stoichiometricrequirement to oxidize the carbon monoxide content of stream 16. Duringnormal operation of the engine 1, relay 36 also transmits a signal toopen valve 29. During elevated temperature operation of engine 1, whenthe exhaust gas is generated at a temperature typically above 700 C,relay 36 transmits a signal to close valve 18 and open valve 22.

Returning to unit 32, during initial low temperature operation of theengine 1, the catalytically treated exhaust gas stream 37 dischargedfrom unit 32 contains a substantial proportion of residual unoxidizedhydrocarbon vapor, which must be recovered to prevent emission to theatmosphere. Stream 37 flows via stream 38, open valve 39 and stream 40into container 41, which contains one or more beds of a suitableabsorbent or adsorbent for hydrocarbon vapors. The hydrocarbon vaporsare thus removed from the exhaust gas stream on or within the discretesolid particles of absorbent or adsorbent within unit 41. Any suitablesolid material to provide the absorption or adsorption function may beprovided within unit 41. Typical usable materials include activatedcarbon such as charcoal, natural or artificial zeolites, activatedalumina, fullers earth, kaolin, organic resins and the like, which maybe employed either singly or in mixtures.

The resulting treated exhaust gas stream 42 discharged downwards fromunit 41 during initial engine operation now has a very low or negligiblecontent of residual hydrocarbon vapors, and during the initial intervalof engine operation the downflowing stream 42 will be essentially freeof hydrocarbon vapors, nitrogen oxides and carbon monoxide. Stream 42may now be safely discharged downwards to atmosphere via stream 43without causing air pollution.

During normal engine operation at elevated temperatures typically in therange of 250 to 700 C, valve 39 is closed and downwards flow throughunit 41 is terminated. Under these conditions, stream 37 flows viastream 44 and valve 45, which is closed during the initial engineoperating period and opened during normal engine operation, when stream37 is essentially free of noxious components. During normal engineoperation, the catalytically treated off-gas thus flows from valve 45via by-pass line 46, which divides into a minor portion which flowsupwards via stream 42 and a major portion which is discharged toatmosphere via stream 43.

The temperature in the absorbent bed within unit 41 is measured bytemperature sensing element 47, which may be similar to element 33described supra. Element 47 transmits a signal to temperature indicatingelement 48 which is similar to unit 34 described supra. Element 48transmits a signal to relay 50, which opens valve 39 and closes valve 45during initial low temperature operation of the engine 1, and closesvalve 39 and opens valve 45 during normal temperature operation of thesystem.

As mentioned supra, during normal operation of the engine 1, stream 46divides into stream 42 and 43. Stream 42 now flows upwards through theabsorbent bed 41, which is now laden with recovered hydrocarbon fromprior low temperature operation as described supra. Stream 42 nowdesorbs hydrocarbon vapor from the absorbent bed within unit 41. Theupwards flow rate of stream 42 is now generally less than 20 percent ofthe overall flow rate of stream .46, and preferably about to percent ofthe stream 46 flow rate. Previously absorbed or adsorbed hydrocarbon inunit 41 is desorbed into the hot exhaust gas portion stream 42 at atemperature typically in the range of 250"v to 700 C. The resultinggaseous mixture of exhaust gas and desorbed hydrocarbon vapor flows fromunit 41 via stream 51 and through valve 52, which is opened by relay 50during normal engine operation, and closed during initial engineoperation, so that during normal engine operation stream 51 flows viaopen valve 52 and stream 4 to the intake appurtenances of engine 1, suchas the air filter 5 or the intake manifold, so that the unburnedhydrocarbon content of stream 51 is at least partially burned in engine1 during normal operation of the engine.

Under extreme overload conditions of engine 1 an exhaust gas temperaturein excess of 1,000 C may be reached. Under these circumstances, relay 36will close both valves 11 and 29 and completely terminate secondary airflow. In addition, relay 50 will close valve 52, so as to terminateupwards flow of stream 42 and thereby prevent overheating and damage tothe hydrocarbon absorbent bed within unit 41. It will be apparent tothose skilled in the art that the functions of relay 50 may be carriedout in some instances by relay 36, in which case units 47, 48, and 50may be omitted. Temperature sensitive and control elements may beprovided at other or alternate places in the system in suitableinstances, to accomplish the control functions described supra.

Numerous alternatives within the scope of the present invention, besidesthose alternatives mentioned supra, will occur to those skilled in theart. Secondary air streams 10 and 28 may be provided by a singlesecondary air blower, and in any case the secondary air blow ers will beprovided with appropriate pressure valves or the like. Thetemperature-responsive control systems described supra may be replacedby suitable functionally equivalent devices or equipment in suitableinstances. Thus, the operation may alternatively be controlled by timecycle relays or the like, so that valve 11 is fully open and valve 29 isclosed during the first 10 minutes or so after startup of a cold engine,or during the first 2 to 6 minutes after startup when ambienttemperatures are normal or relatively high. Then, after this initialtime period, typically 4 minutes in duration, the valve settings wouldbe changed by a time control relay initially activated by the startercircuit or the like, to automatically open valve 29 and to partially ortotally close valve 11. The temperature ranges and other limitationsenumerated supra may vary, depending on the type of engine, the natureof the fuel, the nature or type of catalyst employed in units 24 and/or32, and the nature of the hydrocarbon absorbent employed in unit 41.Thus, some absorbents such as activated carbon are adversely affected byelevated temperature, and when such absorbents are employed in unit 41,the valve 5 2 may be closed at relatively lower temperatures such as 600C. In some instances, such as described in US. Patent Application No.33,359 filed Apr. 30, 1970, new US. Pat. No. 3,656,915, the reducing andoxidizing catalyst beds will be integrally combined into a single devicesuch as a catalytic muffler, and the same catalytic agent, known as aredox catalyst because of ability to catalyze both reducing andoxidizing reactions, may be employed in both catalyst beds. Thetemperature sensing element 33 may measure exhaust gas temperature priorto the oxidizing catalyst bed. In any alternative of this nature, theoperating parameter of exhaust gas temperature is measured so as tocontrol the settings of the valves 11, 18, 22, 29, 39, 45 and/or 52. Insome instances, valve 52 may be open during the initial engine operatingperiod.

An example of the application of the method of the present invention toan automobile engine will now be described.

Example The present system was applied to a 350 cu. in. Oldsmobile 1971Model engine. The internal combustion engine tested had the followingparameters:

Automatic Transmission Spark Control The engine was startedin accordancewith the normal manufacturers recommended procedure.

TABLE 1.COLD ENGINE STARTUPFIRST TIME PERIOD Concentration in vol.percent Flow Engine Hydro- Stream rate, 'Iemrx, speed, carbons No.c.i.m. C. m.p.h. as hexane N0;

Ambient Idle At C., 1 atm.

TABLE II.NO RMAL ENGINE OPERATION-SECOND TIME PERIOD Concentration invol. percent Flow Engine Hydro- Stream rate, Temrx, speed, carbons No.c.t.n1 C. m.p.h. as hexane 00 N0;

TABLE III.-OVERLOAD ENGINE OPERATIONTHIRD TIME PERIOD Concentration invol. percent Flow Engine Hydro- Stre rate, Temp speed, carbons N0.c.i.m. m.p.h. as hexane 00 NO,

We claim:

1. In a method for controlling engine exhaust emissions in which theinitial exhaust gas stream emitted by the engine contains noxiousimpurities including nitrogen oxides, hydrocarbons and carbon monoxide,said initial exhaust gas stream is passed through a reducing catalystbed for the catalytic reduction of nitrogen oxides to nitrogen, theintermediate exhaust gas stream discharged from said reducing catalystbed is passed through an oxidizing catalyst bed for the catalyticoxidation of at least a portion of said hydrocarbons and carbon monoxideto innocuous oxidation products, secondary air being added to saidexhaust gas stream prior to passing the exhaust gas stream through saidoxidizing catalyst bed, and a resulting catalytically treated exhaustgas stream is discharged from said oxidizing catalyst bed, theimprovement during successive time periods of operation of said engineafter startup which comprises a. operating said engine during a firsttime period, said first time period commencing with engine startup andextending for a duration of up to about 10 minutes, said initial exhaustgas stream being emitted at a temperature below 250 C and containing anabnormally high concentration of hydrocarbon vapor during said firsttime period,

b. injecting a first stream of secondary air into said initial exhaustgas stream during said first time period, s id fifi gsts at sec ar airlnes i jected prior to passing said initial exhaust gas stream throughsaid reducing catalyst bed,

c. contacting said resulting catalytically treated exhaust gas streamwith a solid absorbent bed during said first time period, wherebyresidual hydrocarbon vapor in said resulting exhaust gas stream is absorbed by said solid absorbent bed and a final exhaust gas streamsubstantially free of hydrocarbon vapor is discharged from said solidabsorbent bed,

d. operatingsaid engine under normal operating conditions during asecond time period after the termination of said first time period, saidinitial exhaust gas stream being emitted from said engine at atemperature in the range of 250? to 700 C during said second timeperiod,

c. reducing the flow rate of said first stream of secondary air duringsaid second time period, whereby the free oxygen content of said initialexhaust gas stream at entry into said reducing catalyst bed is less thanabout 30 percent in excess of the stoichiometric requirement to oxidizecarbon monoxide contained in said initial exhaust gas stream,

f. injecting a second stream of secondary air into said intermediateexhaust gas stream during said second time period, said second stream ofsecondary air being injected prior to passing said intermediate exhaustgas stream through said oxidizing catalyst bed, whereby substantiallyall of the hydrocarbon vapor and carbon monoxide in said exhaust gasstream are catalytically oxidized in said oxidizing catalyst bed duringsaid second time period,

. dividing the resulting catalytically treated exhaust gas streamdischarged from said oxidizing catalyst bed during said second timeperiod into a major portion and a minor portion,

h. discharging said major portion of said resulting catalyticallytreated exhaust gas stream to atmosphere during said second time period,discharged from said absorbent bed passing said minor portion of saidresulting catalytically treated exhaust gas stream through saidabsorbent bed during said second time period, whereby hydrocarbonpreviously absorbed during said first time period is desorbed and amixed gaseous stream containing desorbed hydrocarbon vapor and exhaustgas is dischargedfrom saidasorbent bPd during said second time period,and

j. passing said mixed gaseous stream formed by step (i) into said engineduring said second time period,

whereby at least a portion of the desorbed hydrocarbon vapor in saidmixed gaseous stream is burned in said engine.

2. The method of claim 1, in which said engine is an internal combustionengine.

3. The method of claim 2, in which said internal combustion engine is anautomobile engine.

4. The method of claim 1, in which said reducing catalyst bed and saidoxidizing catalyst bed contain an active catalytic agent selected fromthe group consisting of nickel, cobalt, copper and manganese, andmixtures thereof, deposited on a carrier.

5. The method of claim l, in which said solid absorbent bed contains anactive hydrocarbon adsorbent selected from the group consisting ofactivated carbon, zeolite, activated alumina, fullers earth, kaolin, andorganig; resin and mixtures thereof.

6. The method of claim l, in which rsnseainm air stream is injected intosaid initial exhaust gas stream according to step (b) by injecting saidsecondary air stream into the exhaust manifold of said engine.

7. The method of claim 1, in which the duration of said firt time periodis in the range of about 2 to 6 minutes.

8. in a method for controlling engine exhaust emissions in which theinitial exhaust gas stream emitted by the engine contains noxiousimpurities including nitrogen oxides, hydrocarbons and carbon monoxide,said initial exhaust gas stream is passed through a reducing catalystbed for the catalytic reduction of nitrogen oxides to nitrogen, theintermediate exhaust gas stream discharged from said reducing catalystbed is passed through an oxidizing catalyst bed for the catalyticoxidation of at least a portion ofsaid hydrocarbons and carbon monoxideto innocuous oxidation products, secondary air being added to saidexhaust gas stream prior to passing the exhaust gas stream through saidoxidizing catalyst bed, and a resulting catalytically treated exhaustgas stream is discharged from said oxidizing catalyst bed, theimprovement during successive time periods of operation of said engineincluding operation at an abnormally high temperature which comprises a.operating said engine under normal operating conditions, whereby saidinitial exhaust gas stream is emitted from said engine at a normaloperating temperature in the range of 250 to 700 C,

b. injecting a first stream of secondary air into said initial exhaustgas stream under normal operating conditions, said first stream ofsecondary air being injected prior to passing said initial exhaust gasstream through said reducing catalyst bed, whereby the free oxygencontent of said initial exhaust gas stream at entry into said reducingcatalyst bed is less than about 30 percent in excess of thestoichiometric requirement to oxidize carbon monoxide contained in saidinitial exhaust gas stream,

0. injecting a second stream of secondary air into said intermediateexhaust gas stream under normal operating conditions, said second streamof secondary air being injected prior to passing said intermediateexhaust gas stream through said oxidizing catalyst bed, wherebysubstantially all of the hydrocarbon vapor and carbon monoxide in saidexhaust gas stream are catalytically oxidized in said oxidizing catalystbed under normal operating conditions,

d. operating said engine under abnormal operating conditions during afirst time period after normal operation of said engine, whereby saidinitial exhaust gas stream is emitted from said engine at a temperaturein the range of 700 to l,000 C during said first time period,

c. cooling said initial exhaust gas stream by indirect heat exchangewith the surrounding atmosphere during said first time period, bypassing said initial exhaust gas stream through means adapted to receiveand cool exhaust gas during said first time period,

f. maintaining steps (b) and (c) during said first time period,

g. operating said engine under abnormal operating conditions during asecond time period after the termination of said first time period,whereby said initial exhaust gas stream is emitted from said engine at atemperature above 1,000 C during said second time period, and

h. terminating the flow of said first and second streams of secondaryair during said second time period.

9. The method of claim 8, in which said engine is an internal combustionengine.

10. The method of claim 9, in which said internal combustion engine isan automobile engine.

11. The method of claim 8, in which said reducing catalyst bed and saidoxidizing catalyst bed contain an active catalytic agent selected fromthe group consisting of nickel, cobalt, copper and manganese, andmixtures thereof, deposited on a carrier.

12. The method of claim 8, in which said first stream of secondary airis injected into said initial exhaust gas stream according to step (b)by injecting said secondary air stream into the exhaust manifold of saidengine.

13. in a method for controlling engine exhaust emissions in which theinitial exhaust gas stream emitted by the engine contains noxiousimpurities including nitrogen oxides, hydrocarbons and carbon monoxide,said initial exhaust gas stream is passed through a reducing catalystbed for the catalytic reduction of nitrogen oxides to nitrogen, theintermediate exhaust gas stream discharged from said reducing catalystbed is passed through an oxidizing catalyst bed for the catalyticoxidation of at least a portion of said hydrocarbons and carbon monoxideto innocuous oxidation products, secondary air being added to saidexhaust gas stream prior to passing the exhaust gas stream through saidoxidizing catalyst bed, and a resulting catalytically treated exhaustgas stream is discharged from said oxidizing catalyst bed, theimprovement during successive time periods of operation of said engineafter startup which comprises a. operating said engine during a firsttime period, said first time period commencing with engine startup andextending for a duration of up to about 10 minutes, said initial exhaustgas stream being emitted at a temperature below 250 C and containing anabnormally high concentration of hydrocarbon vapor during said firsttime period,

b. injecting a first stream of secondary air into said initial exhaustgas stream during said first time period, said first stream of secondaryair being injected prior to passing said initial exhaust gas streamthrough said reducing catalyst bed,

c. contacting said resulting catalytically treated exhaust gas streamwith a solid absorbent bed during said first time period, wherebyresidual hydrocarbon vapor in said resulting exhaust gas stream is ab-13 sorbed by said solid absorbent bed and final exhaust gas streamsubstantially free of hydrocarbon vapor is discharged from said solidabsorbent bed,

. operating said engine under normal operating conditions during asecond time period after the termination of said first time period, saidinitial exhaust gas stream being emitted from said engine at atemperature in the range of 250 to 700 C during said second time period,

. reducing the flow rate of said first stream of secondary air duringsaid second time period, whereby the free oxygen content of said initialexhaust gas stream at entry into said reducing catalyst bed is less thanabout 30 percent in excess of thestoichiq metric requirement to oxidizecarbon monoxide contained in said initial exhaust gas stream, injectinga second stream of secondary air into said intermediate gas streamduring said second time period, said second stream of secondary airbeing injected prior to passing said intermediate exhaust gas streamthrough said oxidizing catalyst bed, whereby substantially all of thehydrocarbon vapor and carbon monoxide in said exhaust gas stream arecatalytically oxidized in said oxidizing catalyst bed during said secondtime period,

g. dividing the resulting catalytically treated exhaust gas streamdischarged from said oxidizing catalyst bed during said second timeperiod into a major portion and a minor portion,

h. discharging said major portion of said resulting catalyticallytreated exhaust gas stream to atmosphere during said second time period,

. passing said minor portion of said resulting catalytipassing saidmixed gaseous stream formed by step (i) into said engine during saidsecond time period, whereby at least a portion of the desorbedhydrocarbon vapor in said mixed gaseous stream is burned in said engine,

k. operating said engine under abnormal operating conditions during athird time period after the termination of said second time period,whereby said initial exhaust gas stream is emitted from said engine at atemperature in the range of 700 to l,000 C during said third timeperiod,

l. cooling said initial exhaust gas stream by indirect heat exchangewith the surrounding atmosphere during said third time period, bypassing said initial exhaust gas stream through means adapted to receiveand cool exhaust gas during said third time period,

m. maintaining steps (e), (f), (g), (h), (i) and (j) during said thirdtime period,

n. operating said engine under abnormal operating conditions during afourth time period after the termination of said third time period,whereby said initial exhaust gas stream is emitted from said engine at atemperature above l,000 C during said fourth time period,

o. terminating the flow of said first and second streams of secondaryair during said fourth time period, and

p. terminating the flow of said minor portion of said resultingcatalytically treated exhaust gas stream through said absorbent bedduring said fourth time period, and thereby terminating the flow of saidmixed gaseous stream into said engine during said fourth time period.

14. The method of claim 13, in which said engine is an internalcombustion engine.

15. The method of claim 14, in which. said internal combustion engine isan automobile engine.

16. The method of claim 13, in which said reducing catalyst bed and saidoxidizing catalyst bed contain an active catalyticagent selected fromthe group consisting of nickel, cobalt, copper and manganese, andmixtures thereof, deposited on a carrier.

17. The method of claim 13, in which said solid absorbent bed containsan active hydrocarbon absorbent selected from the group consisting ofactivated carbon, zeolite, activated alumina, fullers earth, kaolin, andorganic resin, and mixtures thereof.

18. The method of claim 13, in which said first stream of secondary airis injected into said initial exhaustgas stream according to step (b) byinjecting said secondary air stream into the exhaust manifold of saidengine.

19. The method of claim 13, in which the duration of said first timeperiod is in the range of about 2 to 6 minutes.

20. The method of claim 13, in which the flow of said first stream ofsecondary air is terminated during said second time period.

UNITED STATES PATENT (NFMQE QCHCRT E HI/VH1 H t 11. o R R W TH WM Patent3, 757,521 Dated September 11, 1973 Inventor(s) John F. Tourtellotte eta1 It is certified. that error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

Claim 1 step (h) at col. 10 lines 54-55, delete "discharged from saidabsorbent bed Q Also step (i) at cola 10 lines 62=63 delete"dischargedfrom saidasorb==ent bPd" and read "discharged from saidabsorbent bedo Claim 5 line 2 at col, 11 line 11, delete "adsorbent" andread "absorbent".

Claim 13 step (f after the first intermediate at c010 13 line 18, readexhausto Signed and sealed this 18th day of December 1973a (SEAL)Attest:

EDWARD MG FLETCHER J30 RENE D 0 TEGTMEYER Attesting Gfficer ActingCommissioner of Patents

1. In a method for controlling engine exhaust emissions in which theinitial exhaust gas stream emitted by the engine contains noxiousimpurities including nitrogen oxides, hydrocarbons and carbon monoxide,said initial exhaust gas stream is passed through a reducing catalystbed for the catalytic reduction of nitrogen oxides to nitrogen, theintermediate exhaust gas stream discharged from said reducing catalystbed is passed through an oxidizing catalyst bed for the catalyticoxidation of at least a portion of said hydrocarbons and carbon monoxideto innocuous oxidation products, secondary air being added to saidexhaust gas stream prior to passing the exhaust gas stream through saidoxidizing catalyst bed, and a resulting catalytically treated exhaustgas stream is discharged from said oxidizing catalyst bed, theimprovement during successive time periods of operation of said engineafter startup which comprises a. operating said engine during a firsttime period, said first time period commencing with engine startup andextending for a duration of up to about 10 minutes, said initial exhaustgas stream being emitted at a temperature below 250* C and containing anabnormally high concentration of hydrocarbon vapor during said firsttime period, b. injecting a first stream of secondary air into saidinitial exhaust gas stream during said first time period, said firststream of secondary air being injected prior to passing said initialexhaust gas stream through said reducing catalyst bed, c. contactingsaid resulting catalytically treated exhaust gas stream with a solidabsorbent bed during said first time period, whereby residualhydrocarbon vapor in said resulting exhaust gas stream is absorbed bysaid solid absorbent bed and a final exhaust gas stream substantiallyfree of hydrocarbon vapor is discharged from said solid absorbent bed,d. operating said engine under normal operating conditions during asecond time period after the termination of said first time period, saidinitial exhaust gas stream being emitted from said engine at atemperature in the range of 250* to 700* C during said second timeperiod, e. reducing the flow rate of said first stream of secondary airduring said second time period, whereby the free oxygen content of saidinitial exhaust gas stream at entry into said reducing catalyst bed isless than about 30 percent in excess of the stoichiometric requirementto oxidize carbon monoxide contained in said initial exhaust gas stream,f. injecting a second stream of secondary air into said intermediateexhaust gas stream during saId second time period, said second stream ofsecondary air being injected prior to passing said intermediate exhaustgas stream through said oxidizing catalyst bed, whereby substantiallyall of the hydrocarbon vapor and carbon monoxide in said exhaust gasstream are catalytically oxidized in said oxidizing catalyst bed duringsaid second time period, g. dividing the resulting catalytically treatedexhaust gas stream discharged from said oxidizing catalyst bed duringsaid second time period into a major portion and a minor portion, h.discharging said major portion of said resulting catalytically treatedexhaust gas stream to atmosphere during said second time period,discharged from said absorbent bed i. passing said minor portion of saidresulting catalytically treated exhaust gas stream through saidabsorbent bed during said second time period, whereby hydrocarbonpreviously absorbed during said first time period is desorbed and amixed gaseous stream containing desorbed hydrocarbon vapor and exhaustgas is dischargedfrom saidasorbent bPd during said second time period,and j. passing said mixed gaseous stream formed by step (i) into saidengine during said second time period, whereby at least a portion of thedesorbed hydrocarbon vapor in said mixed gaseous stream is burned insaid engine.
 2. The method of claim 1, in which said engine is aninternal combustion engine.
 3. The method of claim 2, in which saidinternal combustion engine is an automobile engine.
 4. The method ofclaim 1, in which said reducing catalyst bed and said oxidizing catalystbed contain an active catalytic agent selected from the group consistingof nickel, cobalt, copper and manganese, and mixtures thereof, depositedon a carrier.
 5. The method of claim 1, in which said solid absorbentbed contains an active hydrocarbon adsorbent selected from the groupconsisting of activated carbon, zeolite, activated alumina, fuller''searth, kaolin, and organic resin, and mixtures thereof.
 6. The method ofclaim 1, in which said secondary air stream is injected into saidinitial exhaust gas stream according to step (b) by injecting saidsecondary air stream into the exhaust manifold of said engine.
 7. Themethod of claim 1, in which the duration of said firt time period is inthe range of about 2 to 6 minutes.
 8. In a method for controlling engineexhaust emissions in which the initial exhaust gas stream emitted by theengine contains noxious impurities including nitrogen oxides,hydrocarbons and carbon monoxide, said initial exhaust gas stream ispassed through a reducing catalyst bed for the catalytic reduction ofnitrogen oxides to nitrogen, the intermediate exhaust gas streamdischarged from said reducing catalyst bed is passed through anoxidizing catalyst bed for the catalytic oxidation of at least a portionof said hydrocarbons and carbon monoxide to innocuous oxidationproducts, secondary air being added to said exhaust gas stream prior topassing the exhaust gas stream through said oxidizing catalyst bed, anda resulting catalytically treated exhaust gas stream is discharged fromsaid oxidizing catalyst bed, the improvement during successive timeperiods of operation of said engine including operation at an abnormallyhigh temperature which comprises a. operating said engine under normaloperating conditions, whereby said initial exhaust gas stream is emittedfrom said engine at a normal operating temperature in the range of 250*to 700* C, b. injecting a first stream of secondary air into saidinitial exhaust gas stream under normal operating conditions, said firststream of secondary air being injected prior to passing said initialexhaust gas stream through said reducing catalyst bed, whereby the freeoxygen content of said initial exhaust gas stream at entry into saidreducing catalyst bed is less than about 30 percent in excess of thestoichiometric requirement to oxidize carbon monoxide contained in saidinitIal exhaust gas stream, c. injecting a second stream of secondaryair into said intermediate exhaust gas stream under normal operatingconditions, said second stream of secondary air being injected prior topassing said intermediate exhaust gas stream through said oxidizingcatalyst bed, whereby substantially all of the hydrocarbon vapor andcarbon monoxide in said exhaust gas stream are catalytically oxidized insaid oxidizing catalyst bed under normal operating conditions, d.operating said engine under abnormal operating conditions during a firsttime period after normal operation of said engine, whereby said initialexhaust gas stream is emitted from said engine at a temperature in therange of 700* to 1,000* C during said first time period, e. cooling saidinitial exhaust gas stream by indirect heat exchange with thesurrounding atmosphere during said first time period, by passing saidinitial exhaust gas stream through means adapted to receive and coolexhaust gas during said first time period, f. maintaining steps (b) and(c) during said first time period, g. operating said engine underabnormal operating conditions during a second time period after thetermination of said first time period, whereby said initial exhaust gasstream is emitted from said engine at a temperature above 1,000* Cduring said second time period, and h. terminating the flow of saidfirst and second streams of secondary air during said second timeperiod.
 9. The method of claim 8, in which said engine is an internalcombustion engine.
 10. The method of claim 9, in which said internalcombustion engine is an automobile engine.
 11. The method of claim 8, inwhich said reducing catalyst bed and said oxidizing catalyst bed containan active catalytic agent selected from the group consisting of nickel,cobalt, copper and manganese, and mixtures thereof, deposited on acarrier.
 12. The method of claim 8, in which said first stream ofsecondary air is injected into said initial exhaust gas stream accordingto step (b) by injecting said secondary air stream into the exhaustmanifold of said engine.
 13. In a method for controlling engine exhaustemissions in which the initial exhaust gas stream emitted by the enginecontains noxious impurities including nitrogen oxides, hydrocarbons andcarbon monoxide, said initial exhaust gas stream is passed through areducing catalyst bed for the catalytic reduction of nitrogen oxides tonitrogen, the intermediate exhaust gas stream discharged from saidreducing catalyst bed is passed through an oxidizing catalyst bed forthe catalytic oxidation of at least a portion of said hydrocarbons andcarbon monoxide to innocuous oxidation products, secondary air beingadded to said exhaust gas stream prior to passing the exhaust gas streamthrough said oxidizing catalyst bed, and a resulting catalyticallytreated exhaust gas stream is discharged from said oxidizing catalystbed, the improvement during successive time periods of operation of saidengine after startup which comprises a. operating said engine during afirst time period, said first time period commencing with engine startupand extending for a duration of up to about 10 minutes, said initialexhaust gas stream being emitted at a temperature below 250* C andcontaining an abnormally high concentration of hydrocarbon vapor duringsaid first time period, b. injecting a first stream of secondary airinto said initial exhaust gas stream during said first time period, saidfirst stream of secondary air being injected prior to passing saidinitial exhaust gas stream through said reducing catalyst bed, c.contacting said resulting catalytically treated exhaust gas stream witha solid absorbent bed during said first time period, whereby residualhydrocarbon vapor in said resulting exhaust gas stream is absorbed bysaid solid absorbent bed and final exhaust gas stream substantially freeof hydrocarbon vapor is discHarged from said solid absorbent bed, d.operating said engine under normal operating conditions during a secondtime period after the termination of said first time period, saidinitial exhaust gas stream being emitted from said engine at atemperature in the range of 250* to 700* C during said second timeperiod, e. reducing the flow rate of said first stream of secondary airduring said second time period, whereby the free oxygen content of saidinitial exhaust gas stream at entry into said reducing catalyst bed isless than about 30 percent in excess of the stoichiometric requirementto oxidize carbon monoxide contained in said initial exhaust gas stream,f. injecting a second stream of secondary air into said intermediate gasstream during said second time period, said second stream of secondaryair being injected prior to passing said intermediate exhaust gas streamthrough said oxidizing catalyst bed, whereby substantially all of thehydrocarbon vapor and carbon monoxide in said exhaust gas stream arecatalytically oxidized in said oxidizing catalyst bed during said secondtime period, g. dividing the resulting catalytically treated exhaust gasstream discharged from said oxidizing catalyst bed during said secondtime period into a major portion and a minor portion, h. dischargingsaid major portion of said resulting catalytically treated exhaust gasstream to atmosphere during said second time period, i. passing saidminor portion of said resulting catalytically treated exhaust gas streamthrough said absorbent bed during said second time period, wherebyhydrocarbon previously absorbed during said first time period isdesorbed and a mixed gaseous stream containing desorbed hydrocarbonvapor and exhaust gas is discharged from said absorbent bed during saidsecond time period, j. passing said mixed gaseous stream formed by step(i) into said engine during said second time period, whereby at least aportion of the desorbed hydrocarbon vapor in said mixed gaseous streamis burned in said engine, k. operating said engine under abnormaloperating conditions during a third time period after the termination ofsaid second time period, whereby said initial exhaust gas stream isemitted from said engine at a temperature in the range of 700* to 1,000* C during said third time period, l. cooling said initial exhaustgas stream by indirect heat exchange with the surrounding atmosphereduring said third time period, by passing said initial exhaust gasstream through means adapted to receive and cool exhaust gas during saidthird time period, m. maintaining steps (e), (f), (g), (h), (i) and (j)during said third time period, n. operating said engine under abnormaloperating conditions during a fourth time period after the terminationof said third time period, whereby said initial exhaust gas stream isemitted from said engine at a temperature above 1,000* C during saidfourth time period, o. terminating the flow of said first and secondstreams of secondary air during said fourth time period, and p.terminating the flow of said minor portion of said resultingcatalytically treated exhaust gas stream through said absorbent bedduring said fourth time period, and thereby terminating the flow of saidmixed gaseous stream into said engine during said fourth time period.14. The method of claim 13, in which said engine is an internalcombustion engine.
 15. The method of claim 14, in which said internalcombustion engine is an automobile engine.
 16. The method of claim 13,in which said reducing catalyst bed and said oxidizing catalyst bedcontain an active catalytic agent selected from the group consisting ofnickel, cobalt, copper and manganese, and mixtures thereof, deposited ona carrier.
 17. The method of claim 13, in which said solid absorbent bedcontains an active hydrocarbon absorbent selected from the groupconsisting of activated carbon, zeoLite, activated alumina, fuller''searth, kaolin, and organic resin, and mixtures thereof.
 18. The methodof claim 13, in which said first stream of secondary air is injectedinto said initial exhaust gas stream according to step (b) by injectingsaid secondary air stream into the exhaust manifold of said engine. 19.The method of claim 13, in which the duration of said first time periodis in the range of about 2 to 6 minutes.
 20. The method of claim 13, inwhich the flow of said first stream of secondary air is terminatedduring said second time period.